01 - Boil pasta in a large pot of salted water until al dente according to package directions. Reserve 1/2 cup pasta water, then drain and set aside.
02 - Heat olive oil and butter over medium heat in a large skillet. Add chopped onion and cook 3–4 minutes until translucent.
03 - Stir in minced garlic and chopped sage leaves; cook 1–2 minutes until fragrant.
04 - Add pumpkin purée, salt, black pepper, and nutmeg to the skillet. Cook 2–3 minutes, stirring frequently.
05 - Pour in heavy cream, stirring until smooth. Simmer gently for 5 minutes to develop flavors.
06 - Add grated Parmesan cheese and stir until fully melted. Adjust thickness by adding reserved pasta water as needed.
07 - Toss drained pasta with sauce in the skillet until evenly coated. Warm together for 1–2 minutes.
08 - Plate immediately, garnished with extra Parmesan and sage if desired.